How the speed it up a portion of a video, and also all of it?
The video gets sped up as you see but it does not affect the length of the strip.  I do not know a way to automate the process but you need to shrink the length of each strip that you are speeding up.  In your case, you are speeding it up by a factor of 4 so you need to make each strip 1/4 of the original length.

Then you need to move all the strips together so there is no space between them.

I did a search on Youtube using this -  blender vse video speed up

and found this video:  https://www.youtube.com/watch?v=NrX1sK_ZQqs

I hope that helps.